Mitsubishi ASX Dodgy Trip Computer & Poor Fuel Economy

When we bought our ASX we went for the 2WD 1.8 DiD Diesel as it was much more responsive than the petrol. While it did cost more we felt that due to its improved fuel efficiency over the petrol variant it would be worth it. The official stats for the car are as follows

Driving lts/100km (mpg)
Urban mode 6.7 (42.2)
Extra urban mode 4.8 (58.9)
Combined mode 5.9 (47.9)

When we first got the car one of the first journeys we did was from Southampton to Wetherby. A nice trip of around 260 miles. Before the journey we filled the tank and then had the trip computer set to “Auto” (which means it gives a rolling average of the last 50km) and through the whole journey the computer was saying > 60mpg. Most of the journey was done between 60-70mph with mostly constant speed.

We made a couple of other short journeys and then filled up the tank… the result – 38,6mpg – Yes thats LESS then quoted Urban value for what is definitely Extra Urban driving. I was expecting it to be AT LEAST into the 50mpg range.

After a few more fill-ups of  equally poor numbers compared to the trip computer ( Real mpg values of 33.1, 40.0, 38.7, 37.2)

This got me thinking to how accurate the trip computer was. After lots of research there was no easy way to get it to give a readout for a “trip”. It would always reset it self every day to 0! After a bit of research I found that you could get the car ECU to not reset from Manual Mode to Auto so this change was made and the car had what most people expect a trip computer to do

This resulted in some very interesting numbers clearly showing that Mitsubishi are not playing ball with the trip computer. Its amazing to see how in-accurate it is considering its one of the simplest things to work out. You only need 2 things. Distance traveled (it knows this from the milometer) and how much petrol its used (it knows how much its injecting).

So far I have done 4.5 full tanks

Distance Trip MPG MPG L/100km Trip Accuracy
357m 48.6 34.5 8.19 40.9%
432m 56.5 37.4 7.55 51.0%
413m 49.2 34.85 41.2%
486m 52.1 39.48 32.0%
294m 54.4 34.15 39.0%

The first 2 tanks included around 220-250 miles of motorway driving =~ half the tank so I would have expected to achieve a rate somewhere around the combined rate = 47.9

So from those numbers we can see that the trip computer was OVER READING by 41.2%, 51.0% and 40.9%

You could ‘maybe’ understand it being 5%? out but those numbers are just silly. My previous car was always within 0.5mpg of the real rate and our Mazda 3 is within 1mpg of the real rate.

Are Mitsubishi trying to pull a fast one – trying to con the media when they test their cars. How many do a real fuel consumption test and how many just rely on the published and trip computer numbers.

Once I have a few more readings I will see what Mitsubishi have to say.

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8 Comments

  1. Hi Rob. I am getting 37.4mpg on average. Funnily enough I did a reverse journey to yourself, Gateshead to Southampton. Filled up before we set off and I was 1/2 home on the return journey before I had to refuel. I have the 1.6 petrol ASX 3. I think my poor return is down to doing an average of 14 miles a day!

  2. Hi Rob, there are lots of comments about the discrepency of computer against mpg on the asxowners site. I do find it difficult to understand how a $billion company with expertese in elecronics, engineering, manufacturing etc can implement such an innacurate device. Im sure its sales exageration/con/gimic at the customers expence. I have a 1.8 2WD DiD Diesel, 22000 miles which regularly returns 46mpg from 20 mile round trip journeys to work on minor roads and some urban. This seems to be about correct for this vehicle. If you cannot achieve thsi I would take back to the garage for investigation .
    Alistair

  3. Hi Rob. I am quite amazed how inaccurate your meter is, and the rubbish control system – hard to believe there isn’t a “Reset” button to start the averaging sequence. My ancient Saab is always within 3% of the value indicated (based on brim to brim tank fills). But are you sure your calculations are correct? The fuel consumption advertised by the manufacturer are from tests done under laboratory conditions and they are conducted/supervised by an independent third party (http://www.dft.gov.uk/vca/vehicletype/type-approval-for-ca.asp ). Though its true that actual driving conditions may well be different from the lab tests, and hence give different results. One of the big problems is the extra urban test, which though done at speeds of up to 75mph, only averages 39mph! – which is hardly representative of Motorway driving. From what I remember, above 50mph, the all important factor is aerodynamics. The Cd for the ASX is listed as 0.32 – remarkably good for a quasi SUV, and the same as my old Saab, which does 40mpg at 70 mph – and it runs on petrol. So your measured results do seem to be rather on the low side. You absolutely sure they are correct?

  4. 100% sure of all my numbers. I have records of all the millage / fill-ups since I have had the car. The in-accuracy of the trip computer is quite staggering.

    The whole ‘official’ mpg numbers gets on my nerves as they are the most unrealistic numbers ever. Interesting to see what What-Car are doing and the numbers they are seeing. The problem is it means that the trip computer is the only gauge you have to a cars economy when test driving it so its its really out (as in mine) it could really catch you out.

    The consumption is getting a bit better now, still not great but similar to others looking at http://www.spritmonitor.de. I have heard many people see improvements after 5/10K and I am just hitting the 5K mark, so hoping this continues.

  5. Hi Rob, I have had my ASX3 4wd 1.8 diesel since November 2011. 80% motorway driving and am averaging 39mpg. The trip computer on mine is also overstating mpg by approx 10mpg whish is dissapointing. I am planning on taking mine into the dealer shortly if it does not improve after breaking it in.

  6. Rob

    I’ve just bought an ASX2. Having same problem with trip re-setting to AUTO mode.
    Can you tell me how you got it to set on MANUAL mode and stick.

    Thanks

    Lee

  7. How do you reset the trip mileage on the ASX4? Girlfriend just bought an 1.8 diesel ASX4 and she can’t work it out……

  8. Mine is poor too and does not give what the Outlander GX2 gave which was bigger and a lot quicker. My mpg meter claims about 48mpg but is currently sub 40mpg actual. I measure tank to tank every time and have at least 13k miles for each car. Even the Warrior D-ID did better. I have noticed that lower than 10c temperature that mpg takes a dive. It’s going back to the dealers for investigation.

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